The present invention relates generally to an apparatus for inductive signal transfer between the sensing head of a measuring or processing machine and the machine body, and more particularly, to an apparatus for inductive signal transfer between the sensing head of a measuring or processing machine and the machine body wherein the signal is transferred independently of relative motion between the spindle of the machine and the machine body.
A number of measuring and switching sensing heads for measuring machines and machine tools are known in the art. In both measuring machines and machine tools, it is necessary to transfer the signal from the sensing head to an evaluating unit disposed outside of the sensing head.
German Patent Specification DE-OS 23 41 251, for example, discloses a machine tool which uses inductive signal transfer wherein the measuring sensing head is installed in a spindle of the machine. The deflection of the sensing probe of the sensing head is transduced into a proportional electric signal. This electric signal is modulated on a carrier wave and then fed to a transfer coil. The transfer coil is received on the sensing head by means of a ring which includes a groove. The transfer coil cooperates with a receiving coil which is fastened in a groove formed in a projection formed in the spindle casing. The modulated carrier signals after being transferred to the receiving coil are transferred an evaluating unit for further processing.
The ring for receiving the transfer coil is constructed such that it projects-beyond the spindle. This construction has the disadvantage that the ring increases the structural size of the sensing head and therefore makes handling of the sensing head difficult. The transfer coil which is disposed on the ring must cooperate over a relatively narrow air gap with the receiving coil which is disposed on the spindle casing. A constant air gap is difficult to maintain, since the coil carrier is constructed as a ring on the outside of the sensing head. Maintaining this constant air gap is particularly difficult, since the ring and the transfer coil are exposed directly to environmental conditions. Further, since the receiver coil is disposed on the sensing head, if the sensing head is used in a rough environment, interruptions of the transfer interval can easily occur. Further, use of the sensing head in a rough environment may even lead to destruction of the coils.
Therefore, in view of the above, it is an object of the present invention to provide an apparatus with which accurate and trouble-free inductive signal transfer is possible between the sensing head and an arrangement disposed outside of the sensing head.
It is a further object of the present invention to provide an apparatus for inductive signal transfer which may be compactly constructed.
It is still a further object of the present invention to provide an apparatus for inductive signal transfer wherein the coils for the inductive signal transfer are protected against environmental influences during the measuring operation, thereby assuring dependable measuring operation.